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An LC circuit An LC circuit is a variety of resonant circuit or tuned circuit and consists of an inductor, An LC circuit is a variety of resonant circuit or tuned circuit and consists of an inductor, represented by the letter L, represented by the letter L, capacitor, represented by the letter C. capacitor, represented by the letter C. When connected together, an electric current can alternate between them at the circuit's resonant frequency: When connected together, an electric current can alternate between them at the circuit's resonant frequency:

HOW IT WORKS In LC circuit capacitor stores energy in the electric field between its plates, depending on the voltage across it, and an inductor stores energy in its magnetic field, depending on the current through it. If a charged capacitor is connected across an inductor, charge will start to flow through the inductor, building up a magnetic field around it, and reducing the voltage on the capacitor. Eventually all the charge on the capacitor will be gone.

However, the current will continue, because inductors resist changes in current, and energy will be extracted from the magnetic field to keep it flowing. The current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. When the magnetic field is completely dissipated the current will stop and the charge will again be stored in the capacitor (with the opposite polarity) and the cycle will begin again, with the current in the opposite direction. However, the current will continue, because inductors resist changes in current, and energy will be extracted from the magnetic field to keep it flowing. The current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. When the magnetic field is completely dissipated the current will stop and the charge will again be stored in the capacitor (with the opposite polarity) and the cycle will begin again, with the current in the opposite direction.

The energy oscillates back and forth between the capacitor and the inductor until internal resistance makes the oscillations die out. The energy oscillates back and forth between the capacitor and the inductor until internal resistance makes the oscillations die out. The charge flows back and forth between the plates of the capacitor, through the inductor. The charge flows back and forth between the plates of the capacitor, through the inductor. Its action, known mathematically as a harmoni oscillator, is similar to a pendulum swinging back and forth, or water sloshing back and forth in a tank. For this reason the circuit is also called a tank circuit. The oscillations are very fast, hundreds to millions of times per second. Its action, known mathematically as a harmoni oscillator, is similar to a pendulum swinging back and forth, or water sloshing back and forth in a tank. For this reason the circuit is also called a tank circuit. The oscillations are very fast, hundreds to millions of times per second.

Resonance effect The resonance effect occurs when inductive and capacitive reactances are equal. The resonance effect occurs when inductive and capacitive reactances are equal. The frequency at which this equality holds for the particular circuit is called the resonant frequency. The frequency at which this equality holds for the particular circuit is called the resonant frequency.

Series resonance Here R, L, and C are in series in an ac circuit. Inductive reactance (XL) increases as frequency increases while capacitive reactance (XC) decreases with increase in frequency. Here R, L, and C are in series in an ac circuit. Inductive reactance (XL) increases as frequency increases while capacitive reactance (XC) decreases with increase in frequency. At a particular frequency these two reactances are equal in magnitude but opposite in phase. The frequency at which this happens is the resonant frequency (FR). At a particular frequency these two reactances are equal in magnitude but opposite in phase. The frequency at which this happens is the resonant frequency (FR).

Parallel resonance Here a coil (L) and capacitor (C) are connected in parallel with an ac power supply. Here a coil (L) and capacitor (C) are connected in parallel with an ac power supply. Let R be the internal resistance of the coil. When XL equals XC, the reactive branch currents are equal and opposite. Let R be the internal resistance of the coil. When XL equals XC, the reactive branch currents are equal and opposite. Hence they cancel out each other to give minimum current in the main line. Since total current is minimum, in this state the total impedance is maximum Hence they cancel out each other to give minimum current in the main line. Since total current is minimum, in this state the total impedance is maximum

Applications of resonance effect Most common application is tuning. For example, when we tune a radio to a particular station, the LC circuits are set at resonance for that particular carrier frequency. Most common application is tuning. For example, when we tune a radio to a particular station, the LC circuits are set at resonance for that particular carrier frequency. A series resonant circuit provides voltage magnification. A series resonant circuit provides voltage magnification. A parallel resonant circuit provides current magnification. A parallel resonant circuit provides current magnification. A parallel resonant circuit can be used in induction heating A parallel resonant circuit can be used in induction heating